1. Field of the Invention
The present invention is in the field of energy absorbing devices for headboxes used in the manufacture of paper, which headboxes are subjected to low frequency vibration influences from adjoining machinery and the like.
2. Description of the Prior Art
Variation in the basis weight of paper in the machine direction has always been a serious problem in the production of high quality, fine formation paper sheets. The basis weight variation can result from headbox vibration at forced or natural frequencies, which vibration has been transmitted from sources in the vicinity of the box. The headbox vibration must be eliminated in order to produce high quality, uniform, level, basis weight paper sheet and control the levelness throughout sheet production.
There have been numerous disclosures in the prior art for damping vibrational effects in various portions of the papermaking machinery. For example, in U.S. Pat. No. 3,487,720 in which one of the coapplicants herein was the sole inventor, there is described an energy absorbing device for damping flexural vibration of a rotary boring bar. The device consists of a hollow beam which is insertable within the boring bar in which it is desired to damp flexural vibration. The beam has a visco-elastic tube coiled around its periphery, with one end of the tube being sealed. The other end of the tube is connected to an adjustable air supply consisting of a storage tank contained within the beam and a pressure regulator connected from the tank to the tube to supply air to the tube at a regulated pressure. Metal slats are provided along the periphery of the tube throughout the length of the tube and are loosely placed between the tube and the hollow interior of the boring bar in side-by-side relation with respect to each other. These slats are forced against the inside of the boring bar upon inflation of the tube. The slats may be laminated with a visco-elastic material engaging the inside of the boring bar. Weights are placed along the hollow beam to provide an optimum natural frequency vibration ratio between the beam and the boring bar such that the increments of length of the boring bar subjected to the largest amplitudes of transverse vibration are subjected to the largest damping forces.
In U.S. Pat. No. 4,047,676 the applicants herein described a winder or other rotary mechanism including a rotating member such as a rider roll which is subject to vibrations. An energy absorbing vibration damper was connected to the rider roll, the damper including a stationary hollow tube secured along its length to a beam coextensive with the rider roll and a beam member within the stationary tubular member having a resilient hose coiled thereabout. The hose is inflated and a plurality of axially extending metal slats are positioned between the inflatable tube and the inside of the tubular member, the slats being laminated with a visco-elastic material for absorbing vibration of the rider roll.